1. Basic Math and Excel Skill
2. Koch-Glitsch Software
3. Have a Computer
4. Have a Desire
In this part the instructor shows how the following methods could be used to estimate column diameter
1. “C” factor method
This very simple method uses the Souders and Brown equation, which
gives the maximum acceptable vapor velocity below one tray to prevent
excessive entrainment of liquid from this tray to the tray above
Vm = maximum acceptable vapor velocity in the space below one tray,
ρl = liquid density at operating temp. and pressure of the tray (kg/m3),
ρv = vapor density at operating temp. and pressure of the tray (kg/m3),
C = Souders-Brown factor given by figure 12, in m/h versus tray spacing in
cm and liquid surface tension in N/m,
Usual tray spacing: 18 in (46 cm), 24 in (61 cm), 30 in (76 cm). 24 in
(61 cm) is the most frequent particularly for glycol and amine absorbers.
Actually, this spacing also depends on downcomer design.
Instead of figure 12, “C” factor values given by table as follows (from
Campbell – gas Conditioning and Processing) can also be used.
Manufacturers provide specific capacity factors for each proprietary use.
The column diameter of the column is given by equation as follows:
D = inside diameter of the column in meters,
Q = vapor flowrate at actual tray conditions (m3/h),
This method was originally developed for bubble cap trays and gives a
rough diameter value, especially for other types of tray.
2. Nomograph method for valve trays
Manufacturers of valve trays have developed design methods for their
trays. Design procedures are made available for preliminary studies.
Figure 13 is an example of such nomograph method which gives by
simple reading tray diameter with number of pass by tray. It requires the
knowledge for each tray of the liquid flow rate in m3/min and the vapour
load determined with equation as follows:
In this minute the trainer shows in a step-by-step procedure how the exact diameter using excel could be calculated.
Previous nomograph method corresponds to a first approach. It does
not take account of foaming which is the source of major problems in
The Glitsch manual method for Ballast type valve tray gives results
with the following steps:
1st step: Determination of the flow path length (FPL)
An approximate flow path length is useful for establishing the minimum
With the values of the diameter (DT) and the number of pass (NP)
determined with the nomograph method (Figure 13), calculate the flow
path length (FPL) with equation as follows:
2nd step: Determination of Vapor Capacity Factor (CAF)
Figure 14 allows to determine the vapour capacity factor (CAFo) in
meter per second, versus vapor density and tray spacing for nonfoaming
For foaming fluids this vapour capacity factor must be corrected by the
system factor value indicated in the table of figure 15.
Determination of the Downcomer Velocity (VDdsg)
The procedure used in this method for establishing downcomer area is
based on a “design“ velocity in meter per hour given by figure 16 for
non foaming fluid or by equation as follows:
4th step: Determination of Active Area (AAM)
The minimum active area is a function of vapor and liquid loads,
system properties, flood factor and flow path length.
The flood factor (FF) is used in certain equations for purpose of
estimating column size. It is the “design percent of flood” expressed as
A value of not more than 0.77 is normally used for vacuum columns
and a value not more than 0.82 is used for other services.
For demethanisers and near critical point values, it is recommended to
adopt a value in the range 0.6 to 0.7.
These values are intented to give not more than approximately 10 %
Higher flood factorsmay result in excessive entrainment and/or a
column sized too small for effective operation.
A flood factor of 0.65 to 0.75 should be used for column diameters
under 36″ (90 cm).
The minimum active area is determined with equation as follows:
Determination of Active Area (AAM)
5th step: Determination of the Downcomer area (ADM)
The minimum downcomer area is a function of liquid rate, downcomer
design velocity and flood factor.
If the downcomer area calculated by this equation is less than 11 % of
the active area (AAM) adopt for (ADM) the smaller value of relations as
6th step: Determination of the minimum inside diameter (DC) of the
The approximate column cross sectional area is calculated by
equations as follows:
The higher value is adopted.
Minimum inside diameter of the column (DC) in meters is calculated
The instructor in this part aims to help process engineers to reach the followings :
-Become familiar with the environment of KG Tower software
–Know how to Calculate diameter of the tower using KG Tower
–Know how to Calculate other charachteristic of the disigned tower using KG Tower